Astronomers accidentally discover a globular cluster of stars with low metal content

An international group of astronomers led by Soren Larsen (Radbaud University, Netherlands) accidentally discovered a globular cluster that contains very few metals. Astronomers had free time to observe, and they decided to study in more detail the globular cluster in the Andromeda galaxy. Today they will publish their findings in the journal Science.

Globular clusters are usually composed of hundreds of thousands or millions of ancient stars moving in a group across the galaxy. The discovered globular cluster with low metal content is called RBC EXT8 and is located in the Andromeda galaxy. The stars in the cluster contain, on average, 800 times less metals than our Sun.

Astronomers are perplexed by this discovery. Until now, it was believed that large globular clusters must contain a huge amount of metals. The new find casts doubt on the minimum metallicity limit for globular clusters. In addition, this discovery may have implications for theories about the formation of galaxies in the young universe.

The globular cluster RBC EXT8 was originally excluded from the Keck telescope HIRES in Hawaii. However, the researchers had several hours of time left, and they decided to point the telescope at the discovered cluster. They conducted two spectroscopic observations of 20 minutes each to determine the metal content and used three archived images from the Canada-France-Hawaii telescope to determine its size.

Soren Larsen (Radbaud University, Nijmegen, Netherlands) led the study. He kept in touch via Skype with fellow researchers Jean Brody (Swinburne University of Technology, Australia and University of California, USA), Aaron Romanovski (San Jose State University, USA and University of California) and Asher Wasserman (University of California). Wasserman operated a telescope in Hawaii from California.

In the future, researchers hope to find more globular clusters with low metal contents and unravel the mystery of their origin.

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